The solvation force in water, treated as a molecular fluid, confined between two mica surfaces is calculated using molecular dynamics simulations. In order to maintain a constant chemical potential as the wall separation is varied, the mean density of the confined fluid is calculated using a linear superposition approximation. By calculating the chemical potential using the standard test particle method, the approximation is shown to be valid for distances of separation down to about two molecular diameters. Both the density profiles and the solvation force isotherm are oscillatory with a periodicity of about one molecular diameter. The oscillations in structural force show an approximately exponential decay with separation distance.